bindresvport(3)            Library Functions Manual            bindresvport(3)

NAME
       bindresvport - bind a socket to a privileged IP port

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <sys/types.h>
       #include <netinet/in.h>

       int bindresvport(int sockfd, struct sockaddr_in *sin);

DESCRIPTION
       bindresvport()  is  used to bind the socket referred to by the file de-
       scriptor sockfd to a privileged anonymous IP port, that is, a port num-
       ber arbitrarily selected from the range 512 to 1023.

       If  the  bind(2)  performed by bindresvport() is successful, and sin is
       not NULL, then sin->sin_port returns the  port  number  actually  allo-
       cated.

       sin  can  be NULL, in which case sin->sin_family is implicitly taken to
       be AF_INET.  However, in this case, bindresvport() has no way to return
       the port number actually allocated.  (This information can later be ob-
       tained using getsockname(2).)

RETURN VALUE
       bindresvport() returns 0 on success; otherwise -1 is returned and errno
       is set to indicate the error.

ERRORS
       bindresvport() can fail for any of the same reasons as bind(2).  In ad-
       dition, the following errors may occur:

       EACCES The calling process was not privileged (on  Linux:  the  calling
              process  did not have the CAP_NET_BIND_SERVICE capability in the
              user namespace governing its network namespace).

       EADDRINUSE
              All privileged ports are in use.

       EAFNOSUPPORT (EPFNOSUPPORT in glibc 2.7 and earlier)
              sin is not NULL and sin->sin_family is not AF_INET.

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +---------------+---------------+--------------------------------------+
       |Interface      | Attribute     | Value                                |
       +---------------+---------------+--------------------------------------+
       |bindresvport() | Thread safety | glibc >= 2.17: MT-Safe;              |
       |               |               | glibc < 2.17: MT-Unsafe              |
       +---------------+---------------+--------------------------------------+

       The bindresvport() function uses a static variable that  was  not  pro-
       tected by a lock before glibc 2.17, rendering the function MT-Unsafe.

STANDARDS
       Not in POSIX.1.  Present on the BSDs, Solaris, and many other systems.

NOTES
       Unlike  some  bindresvport()  implementations, the glibc implementation
       ignores any value that the caller supplies in sin->sin_port.

SEE ALSO
       bind(2), getsockname(2)

Linux man-pages 6.03              2023-02-05                   bindresvport(3)

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